The present invention relates to the field of cardiac stimulation, and more specifically to the field of stimulating cardiac tissue using a medical electrical lead.
Atrial arrhythmias and supra ventricular tachycardias, such as atrial fibrillation, atrial flutter and atrio-ventricular re-entry, are common post-operative complications among heart surgery patients. It is estimated that during the first seven to ten days after cardiac surgery post-operative supra ventricular tachycardia occurs in up to 63 percent of patients. Aranki et al. showed that patients with postoperative atrial fibrillation have a mean hospital stay of about fifteen days, whereas those patients without post-operative atrial fibrillation have a mean hospital stay of about ten days. Whether such extended hospitalization stays are primarily caused by arrhythmias is not known. See Cardiac Surg. Kirklin J W, Barrat-Boyes BC (Eds.): New York 1993, pg. 210; , xe2x80x9cThe Importance of Age as a Predicator of Atrial Fibrillation and Flutter after Coronary Artery Bypass Graftingxe2x80x9d, Leitch et al., J. Thorac. Cardiovasc. Surg., 1990:100:338-42; xe2x80x9cAtrial Activity During Cardioplegia and Postoperative Arrhythmiasxe2x80x9d, Mullen et al., J. Thorac. Cardiovasc. Surg., 1987:94:558-65.
The presence of such arrhythmias, which in otherwise healthy patients may not be unduly serious, may be especially harmful to heart surgery patients. The surgery itself, the effects of prolonged anesthesia, or both have often already compromised the hemodynamic condition of such patients. Drugs that might be used to prevent post-operative atrial fibrillation are often only partially effective and may have negative effects on cardiac pump function.
Supra ventricular tachycardias may further cause a very irregular ventricular rate, which in turn can lead to hemodynamic conditions deteriorating even further. Such deterioration is especially serious for patients having a compromised left ventricular function. Such complications may also present a serious impediment to the recovery of the patient. See, for example, xe2x80x9cMaintenance of Exercise Stroke Volume During Ventricular Versus Atrial Synchronous Pacing: Role of Contractilityxe2x80x9d, Ausubel et al., Circ., 1985:72(5):1037-43; xe2x80x9cBasic Physiological Studies on Cardiac Pacing with Special Reference to the Optimal Mode and Rate After Cardiac Surgeryxe2x80x9d, Bailer et al., Thorac. Cardiovasc. Surg., 1981:29:168-73.
Due to the serious and potentially life threatening nature of the foregoing conditions, post-operative treatment is often aimed at preventing arrhythmias, such as through the use of drugs. Drugs, however, have been found not always to be effective at preventing arrhythmias. Thus, it is often necessary to provide a means for terminating any arrhythmias, which may occur. One common such means is over-pacing, more about which we say below.
If post-operative atrial fibrillation proves to have unacceptable hemodynamic consequences or causes serious symptoms, and if it does not stop spontaneously or antiarrhythmic drugs are ineffective in treating it, external cardioversion or atrial defibrillation may be required. But external atrial defibrillation, although generally effective as a treatment, may have profound side effects. First, and in contrast to ventricular defibrillation where conversion to normal sinus rhythm may occur after the first shock, atrial defibrillation may not be obtained until after several shocks have been delivered to the patient. This is because ventricular contraction continues during supra ventricular tachycardia. Due to the large amounts of energy, which must be delivered in external defibrillation (e.g., 40 to 360 Joules), the shocks are not tolerated well by conscious patients. External defibrillation is therefore preferably performed under general anesthesia or at least when the patient is sedated. The use of anesthesia gives rise to yet another patient risk factor.
External defibrillation requires relatively high energy because the electrical source is not positioned directly upon the cardiac tissue and instead must pass through the thorax, which tends to dissipate the energy. In contrast, internally applied atrial defibrillation, such as may occur during surgery through defibrillation paddles placed directly on the heart, requires considerably less energy because the defibrillation electrical energy is applied only to the tissue that needs to be defibrillated. In fact, direct atrial defibrillation may be accomplished with only one-Joule pulses in contrast to the 40 Joule and greater pulses required for external defibrillation. See, for example, Kean D., NASPE abs. 246, PACE, Apr.1992, pt. II, pg. 570.
Defibrillation success rates generally depend on the amount of energy delivered. The lower amount of energy delivered, the lower the defibrillation success rate and the greater the number of shocks that must be applied to obtain successful defibrillation. By way of contrast, in direct atrial defibrillation, where energy is applied directly to the heart, the energy level can be selected such that the patient may more easily tolerate both the amount of energy delivered as well as the number of shocks required.
Waldo et al. in xe2x80x9cUse of Temporarily Place Epicardial Atrial Wire Electrodes For The Diagnosis and Treatment of Cardiac Arrhythmias Following Open-Heart Surgery,xe2x80x9d J. Thorac. Cardiovasc. Surg., 1978, vol. 76, no. 4, pp. 558-65 disclose the use of a pair of temporary heart wires placed on the atrium to diagnose and treat arrhythmias through anti-tachycardia overdrive pacing. Specifically, temporary heart wires were sutured to the atrial walls at the time of the heart surgery. Once the patient was ready to be released from hospital, the wires were removed by traction or pulling upon the external end. See, for example, the temporary medical lead disclosed in U.S. Pat. No. 5,527,358 entitled xe2x80x9cTemporary Medical Electrical Leadxe2x80x9d to Mehmanesh et al.,
Temporary post-operative atrial and ventricular pacing with temporary heart wires has been found to successfully treat many post-operative arrhythmias. As such, the procedure has become widespreadxe2x80x94at least 100,000 such procedures are performed each year. The procedure is not without problems, however, even where the most up-to-date heart wires are attached directly to the myocardium. As an example, temporary anti-tachy overdrive pacing is not always effective in terminating postoperative atrial arrhythmias or supra ventricular tachycardias. Improved temporary heart wires are thus required.
The present invention has certain objects. That is, various embodiments of the present invention provide solutions to one or more problems existing in the prior art respecting implantable pacing and/or defibrillation leads and conventional antiarrhythmic, pain-relieving or infection-inhibiting drugs, including one or more of: (a) patients experiencing post-operative arrhythmias and/or pain which may not be adequately treated through the use of temporary medical leads and defibrillatory electrical pulses only; (b) patients experiencing post-operative arrhythmias and/or pain which may not be adequately treated through the use of transvenously or orally delivered anti-arrhythmic or pain relieving drugs, and (c) patients developing post-operative implant-associated bacterial, viral or other infections of the heart.
Various embodiments of the present invention have certain advantages, including one or more of: (a) permitting lower defibrillation energy levels to be employed; (b) permitting fewer defibrillation pulses to be employed; (c) providing more efficient localized delivery of therapeutic or pain-relieving drugs to a patient""s heart, and (d) providing quicker localized delivery of therapeutic or pain-relieving drugs to a patient""s heart.
Various embodiments of the present invention have certain features, including one or more of: (a) a collagen or biodegradable electrode mounting pad loaded with one or more anti-arrhythmic drugs; (b) a collagen or biodegradable electrode mounting pad loaded with one or more pain-relieving drugs; (c) a collagen or biodegradable electrode mounting pad loaded with one or more antibiotic or antiviral drugs; (e) a method of making a drug-loaded collagen or biodegradable electrode mounting pad and associated electrode, and (f) a drug-loaded collagen or biodegradable electrode mounting pad which dissolves and disappears within a patient""s body after a pre-determined post-operative period of time has elapsed which permits the electrical stimulating and drug delivery functions of the pad to have been performed.